This grant is designed to support research which will elucidate the physiological basis for certain distrubances of cardiac rhythm in man and enhance the applicability of that knowledge as a basis for one definitive therapy. The research program is focused principally on 3 disturbances of cardiac rhythm and conduction. The first of these is disturbances ofsinus node function. The second is the Wolff-parkinson- White syndrome. The third is an analysis of the mechanisms and implications of anterior division block. In each instance patients within these diagnostic categories are admitted to the Clinical Research Unit for a period of observation and study. These include routine electrocardiograms and vectorcardiograms, continuous monoritoring of cardiac rhythm in appropriate instances, and a detailed electrophysioloical study based on electrode catheter techniques. The major focus of our interest is on those patients who will ultimately go to cardiac surgery, either for the correction of other abnormalites than those of principal interest or in fact for the surgical treatment of their rhythm distrubance. In the operating room techniques which have been developed here in the animal laboratory are used to map the sequence of epicardial and intramural excitation of both the ventricle and the atrium. In some instances these data are basis for subsequent definitive surgery and in other instances represent basic observations for correlation with the preoperative clinical data.